When transporting mounds of soil from one side of a garden to the other, the best way to do that is with a wheelbarrow. It’s understandable that many of us say the incorrect wheelbarrel since barrel is a word, and if the barrel is big enough, it certainly could hold a lot of soil, but the correct word is wheelbarrow.
According to the Online Etymology Dictionary, one of the oldest meanings for barrow is a vehicle for carrying a load, c.1300, barewe, probably from an unrecorded O.E. *bearwe basket, barrow, from beran, to bear, to carry.
Add a couple of wheels onto that barrow, and wheelbarrow makes perfect sense.